Three-dimensional composite current collector and its preparation method and application

Abstract

This application belongs to the technical field of lithium metal batteries, and particularly relates to a three-dimensional composite current collector and its preparation method and application. The three-dimensional composite current collector includes a foam metal and a nano-metal hydroxide layer at least bonded to the porous surface of the foam metal, and a carbon layer is further bonded to the surface of the nano-metal hydroxide layer facing away from the foam metal. Depositing the nano-metal hydroxide layer on the surface of the foam metal further increases the surface area of the three-dimensional composite current collector, thereby dispersing the current density and slowing down the volume expansion. The carbon layer bonded to the surface of the nano-metal hydroxide layer can react with lithium to form a lithiumophilic structure of LiC6 and LiOH, homogenize the lithium ion flow, is beneficial to the morphology control of the lithium metal negative electrode during the cycling process, can relieve the volume expansion during the charge and discharge process of the battery and inhibit the growth of dendrites, and improve the cycle life of the battery.

Description

Technical Field

[0001] This application belongs to the technical field of lithium metal batteries, and particularly relates to a three-dimensional composite current collector and its preparation method and application. Background Art

[0002] Since the birth of lithium-ion batteries, with advantages such as high energy density, environmental friendliness, high safety performance, and low self-discharge, they have become an important application direction in current fields such as power batteries, high-power electronic devices, and portable devices.

[0003] Although lithium-ion batteries have achieved great development in the field of new energy technologies, with the increasing demand for electronic devices and the frequency of use, the existing lithium-ion batteries are getting closer and closer to the theoretical energy density. Therefore, to meet the needs of human development, lithium metal batteries have characteristics such as high theoretical energy density (3860 mAh / g), low reduction potential (-3.04 V vs. standard hydrogen potential), and low density, and are expected to become one of the potential high-energy density batteries.

[0004] As an important research direction of lithium metal batteries, lithium metal anodes still face many problems, mainly including the following aspects: during the cyclic charge and discharge process, the lithium metal anode will produce obvious volume expansion. Due to the difference in local current distribution, dendritic morphologies will appear on the surface of the lithium metal anode. As the dendrites grow continuously, they will pierce the separator and contact the cathode, causing a short circuit; the reduction potential of the lithium metal anode is -3.04 V, with a low electrode potential, strong reducibility, high reaction activity, and it can react with most electrolytes, and is prone to react with the electrolyte to form a solid electrolyte (SEI) film. As the volume of the lithium metal anode changes during the cyclic charge and discharge, the continuous formation of the SEI film will occur. This phenomenon will continuously consume the lithium metal anode and the electrolyte, reducing the Coulombic efficiency of the lithium metal battery; during the battery cycle process, the lithium metal will break to form dead lithium, reducing the battery cycle life. Summary of the Invention

[0005] The purpose of this application is to provide a three-dimensional composite current collector and its preparation method and a lithium battery anode, aiming to solve the problems of low Coulombic efficiency, poor working stability, and low cycle life of the current collector of the existing lithium battery anode to a certain extent.

[0006] To achieve the above application purpose, the technical solutions adopted in this application are as follows:

[0007] In the first aspect, this application provides a three-dimensional composite current collector, including a foam metal and a nano-metal hydroxide layer at least combined on the porous surface of the foam metal, and a carbon layer is also combined on the surface of the nano-metal hydroxide layer facing away from the foam metal.

[0008] Preferably, the metallic foam includes at least one of nickel foam, aluminum foam, and copper foam; and / or

[0009] The nano-metal hydroxide layer includes at least one of a nano-nickel hydroxide layer, a nano-aluminum hydroxide layer, a nano-copper hydroxide layer, a nano-magnesium hydroxide layer, a nano-vanadium hydroxide layer, a nano-cobalt hydroxide layer, a nano-molybdenum hydroxide layer, a nano-iron hydroxide layer, and a nano-zinc hydroxide layer; and / or

[0010] The carbon layer includes at least one of vertically aligned graphene and nano-carbon.

[0011] Preferably, the nano-metal hydroxide particles of the nano-metal hydroxide layer are nano-sheets.

[0012] In a second aspect, the present application provides a method for preparing a three-dimensional composite current collector, including the following steps:

[0013] Perform a precipitation reaction on the metallic foam, soluble metal salt, and pH regulator in a solvent to obtain a nano-metal hydroxide / metallic foam composite current collector;

[0014] Perform carbon layer deposition treatment on the nano-metal hydroxide / metallic foam composite current collector to obtain a carbon-coated nano-metal hydroxide / metallic foam composite current collector.

[0015] Preferably, the precipitation reaction is a hydrothermal reaction; and / or

[0016] When performing the precipitation reaction, a morphology regulator is further added to the solvent; and / or

[0017] The pH of the precipitation reaction is 10-11, and the reaction temperature is 50°C-120°C; and / or

[0018] The carbon layer deposition treatment is performed in carbon hydrogen gas; and / or

[0019] The treatment temperature of the carbon layer deposition treatment is 300°C-900°C.

[0020] Preferably, the soluble metal salt includes at least one of a soluble nickel salt, a soluble aluminum salt, a soluble copper salt, a soluble magnesium salt, a soluble vanadium salt, a soluble cobalt salt, a soluble molybdenum salt, a soluble iron salt, and a soluble zinc salt; and / or

[0021] The pH regulator includes at least one of hexamethylenetetramine, urea, thiourea, ammonia water, and nickel hydroxide solution; and / or

[0022] The solvent includes at least one of deionized water, ethylene glycol, and N,N-dimethylformamide.

[0023] Preferably, the morphology regulator includes at least one of ammonium fluoride and polyvinylpyrrolidone.

[0024] Preferably, the hydrocarbon gas includes at least one of methane gas and acetylene.

[0025] In a third aspect, the present application provides a negative electrode of a lithium battery, including the three-dimensional composite current collector described above and / or the three-dimensional composite current collector prepared by the above preparation method, an SEI film formed on the surface of the three-dimensional composite current collector, and lithium metal attached to a side of the SEI film facing away from the three-dimensional composite current collector.

[0026] In a fourth aspect, the present application provides a secondary battery, including the negative electrode of the lithium battery described above.

[0027] For the three-dimensional composite current collector provided in the first aspect of the present application, the nano-metal hydroxide layer combined on the porous surface of the foam metal can further increase the surface area of the three-dimensional composite current collector, thereby dispersing the current density and slowing down the volume expansion. At the same time, a carbon layer is also combined on the surface of the nano-metal hydroxide layer facing away from the foam metal, which can react with lithium to form a lithium-philic structure of LiC6 and LiOH, homogenize the lithium ion flow, promote the uniform deposition of metallic lithium, be beneficial to the morphology control of the lithium metal negative electrode during the cycling process, relieve the volume expansion during the charge and discharge process of the battery, and inhibit the growth of dendrites, thereby improving the cycle life of the battery.

[0028] The preparation method provided in the second aspect of the present application has simple steps, easy-to-control parameters, uses materials with low cost and no toxicity, and the obtained nano-metal hydroxide / foam metal composite current collector has excellent performance.

[0029] For the negative electrode of the lithium battery provided in the third aspect of the present application, the dense SEI film on the surface can prevent the secondary reaction between the electrolyte and metallic lithium. At the same time, the SEI film can evenly disperse lithium ions and adjust to achieve a uniform surface ion distribution, promoting the uniform deposition of metallic lithium, thereby inhibiting the growth of lithium dendrites, and further improving the Coulomb efficiency and cycle life of the battery.

[0030] The secondary battery provided in the fourth aspect of the present application includes the negative electrode of the lithium battery described above, has a high Coulomb efficiency, good working stability, and a long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is a surface SEM image of the carbon-coated nano-nickel hydroxide / foam nickel composite current collector provided in Embodiment 1 of the present application, where Figure 1(a) is an SEM image magnified to 500 μm, Figure 1 (b) is an SEM image magnified to 40 μm;

[0033] Figure 2 This is the surface SEM image of the nickel foam current collector provided in Comparative Example 1 of the present application. Among them, Figure 2 (a) is an SEM image magnified to 500 μm, Figure 2 (b) is an SEM image magnified to 40 μm;

[0034] Figure 3 This is the surface SEM image of the nano-nickel hydroxide / nickel foam composite current collector provided in Comparative Example 2 of the present application. Among them, Figure 3 (a) is an SEM image magnified to 500 μm, Figure 3 (b) is an SEM image magnified to 40 μm;

[0035] Figure 4 This is the XRD diffraction pattern of the current collector provided in the examples of the present application;

[0036] Figure 5 This is the nucleation overpotential chart of the current collectors provided in the examples and comparative examples of the present application at a current density of 1 mA cm -2 ;

[0037] Figure 6 This is the Coulomb efficiency diagram of the current collectors provided in the examples and comparative examples of the present application under the current density of 1 mA cm -2 and the capacity test condition of 1 mAh cm -2 ;

[0038] Figure 7 This is the time-voltage curve of the current collectors provided in the examples and comparative examples of the present application under the current density of 1 mA cm -2 and the capacity test condition of 1 mAh cm -2 . Detailed Description of the Invention

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] In the present application, the term "and / or" describes the relationship between associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Among them, A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0041] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0042] It should be understood that in various embodiments of this application, the magnitude of the serial numbers of the above processes does not mean the sequence of execution. Some or all of the steps can be executed in parallel or sequentially. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0043] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments, and are not intended to limit this application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0044] The weight of the relevant components mentioned in the specification of the embodiments of this application not only can refer to the specific content of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the specification of the embodiments of this application is scaled up or down proportionally, it is within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass in the specification of the embodiments of this application can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0045] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of this application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0046] In a first aspect of the embodiments of this application, a three-dimensional composite current collector is provided, including a foam metal and a nano-metal hydroxide layer at least combined on the porous surface of the foam metal.

[0047] The three-dimensional composite current collector provided by the embodiments of the present application, with a nano metal hydroxide layer combined on the porous surface of the foam metal, further increases the surface area of the three-dimensional composite current collector, can disperse the current density and slow down the volume expansion. At the same time, a carbon layer is also combined on the surface of the nano metal hydroxide layer facing away from the foam metal. The carbon-coated nano metal hydroxide layer has lithiophilicity and can react with lithium to form a lithiophilic structure of LiC6 and LiOH, which equalizes the lithium ion flow, promotes the uniform deposition of metallic lithium, is beneficial to the morphology control of the lithium metal negative electrode during the cycling process, can relieve the volume expansion during the charge and discharge process of the battery and inhibit the growth of dendrites, and improve the cycle life of the battery.

[0048] In the embodiments of the present application, the foam metal includes at least one of foam nickel, foam aluminum, and foam copper, which is easy to obtain and has a large surface area, is beneficial to dispersing the current density and slowing down the volume expansion.

[0049] In the embodiments of the present application, the nano metal hydroxide layer includes at least one of a nano nickel hydroxide layer, a nano aluminum hydroxide layer, a nano copper hydroxide layer, a nano magnesium hydroxide layer, a nano vanadium hydroxide layer, a nano cobalt hydroxide layer, a nano molybdenum hydroxide layer, a nano iron hydroxide layer, and a nano zinc hydroxide layer. In a further embodiment of the present application, the nano metal hydroxide particles of the nano metal hydroxide layer are nano-sheets, and the channel structure between the nano-sheets is beneficial to dispersing the current density of the current collector, reducing the local current density, thereby inhibiting the generation of lithium dendrites and the volume expansion generated during the charge and discharge process of the lithium metal negative electrode, and can improve the cycle life and working stability of the battery and improve the performance of the battery.

[0050] In the embodiments of the present application, the carbon layer is two-dimensional nano-carbon, and the two-dimensional nano-carbon includes at least one of, but is not limited to, vertically-aligned graphene (VGA) and nano-carbon. The carbon-coated nano metal hydroxide layer is more lithiophilic than the pure nano metal hydroxide layer and can react with lithium to form a lithiophilic structure of LiC6 and LiOH, which equalizes the lithium ion flow and promotes the uniform deposition of metallic lithium. It should be noted that vertically-aligned graphene is composed of self-assembled and vertically-oriented multi-layer graphene flakes, and is also called carbon nanotube walls and carbon nano flakes. These nano flakes / walls are curved, with a height of about 0.1 - 2 μm and an average thickness of several to more than ten nanometers. They are vertically arranged to form an interconnected network structure. Each vertically-aligned graphene nano flake is composed of multiple stacked graphene flakes. The vertically-oriented graphene can fully utilize the excellent properties of a single graphene flake layer, such as high thermal conductivity and carrier mobility; in addition, the pores between the graphene layers effectively reduce the hindrance to the transmission of ions and molecules in the vertical direction and shorten the transmission path; furthermore, vertically-aligned graphene also has a relatively large specific surface area and rich edges, enhancing its interaction with the external environment.

[0051] The three-dimensional composite current collector provided by the embodiment of the present application has a high-purity, uniform and dense two-dimensional nano metal hydroxide layer formed on the surface of the foam metal and a carbon layer formed on the surface of the two-dimensional nano metal hydroxide layer facing away from the foam metal. It can further increase the specific surface area of the current collector, reduce the local current density, inhibit the volume expansion generated during the charge and discharge process of the three-dimensional composite current collector as a lithium metal negative electrode, and improve the cycle life and working stability of the battery.

[0052] The second aspect of the embodiment of the present application provides a preparation method of a three-dimensional composite current collector, which includes the following steps:

[0053] Perform a precipitation reaction on the foam metal, soluble metal salt, and pH regulator in a solvent to obtain a nano metal hydroxide / foam metal composite current collector;

[0054] Perform carbon layer deposition treatment on the nano metal hydroxide / foam metal composite current collector to obtain a carbon-coated nano metal hydroxide / foam metal composite current collector.

[0055] The preparation method provided by the second aspect of the embodiment of the present application has simple steps, easy-to-control parameters, low material cost, and no toxicity. The obtained nano metal hydroxide / foam metal composite current collector has excellent performance. By means of a precipitation reaction, a two-dimensional nano metal hydroxide is combined on the surface of the foam metal to obtain a uniform and dense nano metal hydroxide layer. The nano metal hydroxide with a high surface area not only greatly increases the specific surface area of the current collector, plays the role of dispersing the current density and slowing down the volume expansion, enhances the Coulomb efficiency and cycle performance of the battery, but also is conducive to inhibiting the generation of lithium dendrites and improving the cycle life of the battery. It should be noted that a carbon layer is deposited and coated on the surface facing away from the bonding surface of the nano metal hydroxide and the foam metal, further improving the lithiophilicity of the current collector, homogenizing the lithium ion flow, promoting the uniform deposition of metallic lithium, and being beneficial to the morphology control of the lithium metal negative electrode during the cycle process.

[0056] In the embodiment of the present application, the foam metal is also pretreated, and the pretreatment includes but is not limited to cleaning with an acid solution, cutting, and drying. Through the pretreatment, impurities on the surface of the foam metal are removed, and it is cut into the required size and shape.

[0057] In the embodiment of the present application, the soluble metal salt includes but is not limited to soluble nickel salt, soluble aluminum salt, soluble copper salt, soluble magnesium salt, soluble vanadium salt, soluble cobalt salt, soluble molybdenum salt, soluble iron salt, soluble zinc salt. In the specific embodiment of the present application, nickel nitrate hexahydrate is selected as the nickel salt, and the raw materials are cheap and easy to obtain.

[0058] In the embodiments of the present application, the pH adjusting agent includes but is not limited to hexamethylenetetramine, urea, thiourea, ammonia water, and nickel hydroxide solution, which is used to adjust the solution pH to 10-11 during the precipitation reaction to make the precipitation reaction more complete.

[0059] In the embodiments of the present application, the solvent includes but is not limited to deionized water, ethylene glycol, and N,N-dimethylformamide, which is used to dissolve and evenly disperse the reactants so that the precipitation reaction proceeds smoothly.

[0060] In the embodiments of the present application, the precipitation reaction is a hydrothermal reaction, and the reaction temperature is 50° C. to 120° C. The formed nano-metal hydroxide has high purity and is evenly dispersed on the surface of the foam metal current collector.

[0061] In the embodiments of the present application, a morphology regulator is added to the solvent during the precipitation reaction. The morphology regulator includes but is not limited to ammonium fluoride and polyvinyl pyrrolidone, which is used to adjust the morphology of the nano-metal hydroxide formed on the surface of the foam metal to obtain a more uniformly dispersed nano-sheet-like metal hydroxide.

[0062] In the embodiments of the present application, the carbon layer deposition process is a chemical vapor deposition process, which can obtain a two-dimensional nanocarbon layer with high purity, good density, small residual stress and good crystallization, that is, upright graphene or nanocarbon.

[0063] In an embodiment of the present application, the chemical vapor deposition process is carried out in a hydrocarbon gas, which includes but is not limited to methane gas and acetylene. The hydrocarbon gas is ionized by plasma, and a two-dimensional nano-carbon layer is deposited and coated on the surface of the nano-metal hydroxide / foam metal composite current collector. In a further embodiment of the present application, the processing temperature of the chemical vapor deposition process is 300°C to 900°C. This temperature range is convenient for ionizing the hydrocarbon gas to form a uniform and dense two-dimensional nano-carbon layer on the surface of the current collector.

[0064] In the specific embodiments of the present application, the above preparation method can be carried out in the following manner but not limited to:

[0065] S1. Cut the nickel foam current collector sheet into a suitable size, remove impurities on the metal substrate with dilute nitric acid, deionized water and ethanol solution, and put it into an oven for drying after cleaning;

[0066] S2, dissolving nickel nitrate hexahydrate, hexamethylenetetramine, and ammonium fluoride in deionized water, and fully mixing them by stirring with a magnetic bar, wherein 2 mmol of nickel nitrate hexahydrate, 1.3 mmol of hexamethylenetetramine, 10 mmol of ammonium fluoride, and 80 ml of deionized water are used, and the pH is adjusted to 10-11;

[0067] S3. Sequentially add the pretreated nickel foam in S1 and the reaction solution prepared in S2 into a polytetrafluoroethylene reaction kettle to completely immerse the nickel foam current collector in the solution, and then carry out a hydrothermal reaction and cool it to room temperature. The temperature of the hydrothermal reaction is 120 °C, and the time of the hydrothermal reaction is 6 h.

[0068] S4. Take out the current collector after the hydrothermal reaction in S3 and put it into an oven to dry overnight to obtain a light green two-dimensional nickel hydroxide / three-dimensional nickel foam composite current collector.

[0069] S5. Place the two-dimensional nickel hydroxide / three-dimensional nickel foam composite current collector prepared in S4 into a plasma chemical vapor deposition tube furnace, evacuate the environment inside the tube to vacuum through a vacuum pump, then introduce methane with a flow rate of 20 sccm after reaching a temperature of 300 °C, wait for the gas flow to stabilize, ionize methane with 300 W plasma, then continue the reaction for 20 min, turn off the plasma device and cool it to room temperature with the furnace empty, and then transfer the current collector sheet after the above reaction to an oven at 60 °C for storage for 360 min to obtain a two-dimensional carbon-coated nickel hydroxide nanosheet composite three-dimensional nickel foam current collector.

[0070] In the third aspect of the embodiments of the present application, a lithium battery negative electrode is provided, including the above three-dimensional composite current collector, a SEI film formed on the surface of the three-dimensional composite current collector, and lithium metal attached to the side of the SEI film facing away from the three-dimensional composite current collector.

[0071] The dense SEI film on the surface of the lithium battery negative electrode provided in the third aspect of the embodiments of the present application can prevent the secondary reaction between the electrolyte and metallic lithium. At the same time, the SEI film can play a role in uniformly dispersing lithium ions and regulating to achieve a uniform surface ion distribution, promoting the uniform deposition of metallic lithium, thereby inhibiting the growth of lithium dendrites and further improving the Coulomb efficiency and cycle life of the battery.

[0072] In the fourth aspect of the present application, a secondary battery is provided, including the above lithium battery negative electrode, having a high Coulomb efficiency, good working stability, and a long cycle life.

[0073] To enable those skilled in the art to clearly understand the above implementation details and operations of the present application, and to significantly reflect the progress performance of the three-dimensional composite current collector and its preparation method and the lithium battery negative electrode in the embodiments of the present application, the following technical solutions are illustrated by multiple examples.

[0074] Example 1: Preparation of carbon-coated nickel hydroxide nanosheet / nickel foam composite current collector

[0075] S1. Sequentially ultrasonically clean the nickel foam sheet with 1 mol / L dilute nitric acid, deionized water, and ethanol solution, and cut it into a pretreated current collector sheet with a size of 5×3.5×1 mm, and then vacuum dry it at a temperature of 60 °C for 360 min.

[0076] S2: Dissolve 2 mmol of nickel nitrate hexahydrate, 1.3 mmol of hexamethylenetetramine, and 10 mmol of ammonium fluoride in 80 ml of deionized water, adjust the pH to 11, and stir for 30 min to obtain a precursor solution.

[0077] S3: Sequentially add the S1 pre-treated current collector sheet and the precursor solution prepared in step S2 into a 100 ml polytetrafluoroethylene reaction kettle, carry out a hydrothermal reaction at 120 °C for 6 h, and then cool to room temperature.

[0078] S4: Alternately rinse the current collector sheet after the reaction in S3 with deionized water, and then transfer the current collector sheet to an oven and store it at 60 °C for 360 min to obtain a two-dimensional nickel hydroxide nanosheet composite nickel foam current collector, that is, a nickel hydroxide / foam nickel composite current collector.

[0079] S5: Place the nickel hydroxide / foam nickel composite current collector into a plasma chemical vapor deposition tube furnace, evacuate the tube environment to vacuum through a vacuum pump, then introduce methane with a flow rate of 20 sccm after reaching a temperature of 300 °C, wait for the gas flow to stabilize, use 300 W plasma to ionize methane, then continue the reaction for 20 min, turn off the plasma device and cool it to room temperature with the furnace empty, and then transfer the current collector sheet after the above reaction to an oven and store it at 60 °C for 360 min to obtain a two-dimensional carbon-coated nickel hydroxide nanosheet composite nickel foam current collector, that is, a carbon-coated nickel hydroxide / foam nickel composite current collector.

[0080] Perform SEM characterization on the surface of the carbon-coated nickel hydroxide / foam nickel composite current collector, and the results are as Figure 1 shown.

[0081] Example 2: Preparation of carbon-coated nickel hydroxide / foam nickel composite current collector

[0082] In step S2, adjust the addition amount of hexamethylenetetramine to make the pH 10;

[0083] In step S3, the hydrothermal reaction is carried out at 50 °C;

[0084] In step S5, introduce methane with a flow rate of 20 sccm after the temperature in the plasma chemical vapor deposition tube furnace reaches 900 °C;

[0085] The remaining steps and parameters are the same as those in Example 1 to obtain a carbon-coated nickel hydroxide / foam nickel composite current collector.

[0086] Example 3: Preparation of carbon-coated nickel hydroxide / foam nickel composite current collector

[0087] In step S2, adjust the addition amount of hexamethylenetetramine to make the pH 10.5;

[0088] In step S3, the hydrothermal reaction is carried out at 80 °C;

[0089] In step S5, after the temperature in the plasma chemical vapor deposition tube furnace reaches 600 °C, methane with a flow rate of 20 sccm is introduced;

[0090] For the remaining steps and parameters, they are the same as those in Example 1, and a carbon-coated nickel hydroxide / foamed nickel composite current collector is prepared.

[0091] Comparative Example 1: Preparation of a foamed nickel current collector

[0092] The foamed nickel sheet is successively ultrasonically cleaned with 1 mol / L dilute nitric acid, deionized water, and ethanol solution and cut into a pretreated current collector sheet of 5 cm × 3.5 cm × 1 mm, and then vacuum dried at 60 °C for 360 min.

[0093] The surface of the foamed nickel current collector is characterized by SEM, and the results are as Figure 2 shown.

[0094] Comparative Example 2:

[0095] S1: The foamed nickel sheet is successively ultrasonically cleaned with 1 mol / L dilute nitric acid, deionized water, and ethanol solution and cut into a pretreated current collector sheet of 5 × 3.5 × 1 mm, and then vacuum dried at 60 °C for 360 min.

[0096] S2: 2 mmol of nickel nitrate hexahydrate, 1.3 mmol of hexamethylenetetramine, and 10 mmol of ammonium fluoride are dissolved in 80 ml of deionized water, and the pH is adjusted to 10 - 11, and stirred for 30 min to prepare a precursor solution.

[0097] S3: The S1 pretreated current collector sheet and the precursor solution prepared in step S2 are successively added to a 100 ml polytetrafluoroethylene reaction kettle, and hydrothermally reacted at 120 °C for 6 h, and then cooled to room temperature.

[0098] S4: The current collector sheet after the completion of the reaction in S3 above is alternately rinsed with deionized water, and then the current collector sheet is transferred to an oven and stored at 60 °C for 360 min to obtain a two-dimensional nickel hydroxide nanosheet composite foamed nickel current collector, that is, a nickel hydroxide / foamed nickel composite current collector.

[0099] The surface of the nickel hydroxide / foamed nickel composite current collector is characterized by SEM, and the results are as Figure 3 shown.

[0100] Furthermore, in order to verify the advancement of the three-dimensional composite current collector of the present application embodiment, the current collectors prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to performance tests by the following method.

[0101] Example 4: Scanning Electron Microscope Detection

[0102] The surface SEM images of the carbon-coated nano nickel hydroxide / nickel foam composite current collector prepared in Example 1, the nickel foam current collector prepared in Comparative Example 1, and the nano nickel hydroxide / nickel foam composite current collector prepared in Comparative Example 2 were taken by a scanning electron microscope respectively. The detection results are shown in Figure 1 , 2 and Figure 3 respectively.

[0103] Among them, Figure 1 is the surface SEM image of the carbon-coated nano nickel hydroxide / nickel foam composite current collector provided in Example 1 of this application;

[0104] Figure 2 is the surface SEM image of the nickel foam current collector provided in Comparative Example 1 of this application;

[0105] Figure 3 is the surface SEM image of the nano nickel hydroxide / nickel foam composite current collector provided in Comparative Example 2 of this application.

[0106] According to Figure 1 , Figure 2 and Figure 3 shown in the surface SEM characterization results and the half-cell test results shown in Table 1, it can be seen that in Example 1, two-dimensional carbon-coated nickel hydroxide nanosheets were formed on the surface of the lithium metal negative electrode current collector. Comparative Example 1 was the original nickel foam, and in Comparative Example 2, two-dimensional nickel hydroxide nanosheets were formed on the surface of the lithium metal negative electrode current collector. Example 1 shows that carbon deposition on the nickel hydroxide nanosheets is beneficial to improving the lithium-philicity of the current collector surface, preventing the diffusion of nickel ions into the electrolyte, and comprehensively improving the battery cycle life and stability; Comparative Example 2 shows that by utilizing the large specific surface area of the nanosheets on the lithium metal negative electrode current collector, the local current density of the lithium metal negative electrode current collector is reduced. As can be seen from Table 1, the two-dimensional carbon-coated nickel hydroxide nanosheet composite nickel foam effectively increases the number of electrode cycles compared with nickel foam.

[0107] Example 5: X-ray Diffraction Detection

[0108] The XRD diffraction patterns of the carbon-coated nano nickel hydroxide / nickel foam composite current collector prepared in Example 1, the nickel foam current collector prepared in Comparative Example 1, and the finished nano nickel hydroxide / nickel foam composite current collector prepared in Comparative Example 2 were detected by an X-ray diffractometer respectively. The main components are Ni(OH)2 and Ni. The detection results are shown in reference to Figure 4 shown.

[0109] According to Figure 4From the XRD diffraction characterization results shown and the half-cell test results shown in Table 1, it can be seen that in Example 1 and Comparative Example 2, there are Ni(OH)2 and Ni characteristic diffraction peaks, while in Comparative Example 1, only Ni characteristic diffraction peaks exist. In the examples of the present application, a reaction solution of nickel source, hexamethylenetetramine and ammonium fluoride is used to grow two-dimensional nickel hydroxide nanosheets on the surface of the nickel foam current collector, so as to effectively disperse the current by increasing the specific surface area, reduce the growth and deposition of lithium dendrites, thereby effectively slowing down the volume expansion caused by deposition and improving the cycle life of the battery; and in Example 1 and Comparative Example 2, in addition to Ni(OH)2 and Ni characteristic diffraction peaks, the content of other impurities in the diffraction peaks is extremely low, which indicates that the two-dimensional nickel hydroxide and two-dimensional carbon-coated nickel hydroxide generated on the surface of the nickel foam current collector have high purity and more excellent current dispersion performance.

[0110] Example 6: Half-cell test

[0111] Directly punch the finished lithium metal negative electrode current collector prepared in Example 1, Comparative Example 1, and Comparative Example 2 into a disk with a diameter of 13 mm as the working electrode with a punching machine, and then use a lithium metal sheet as the counter electrode, a Celgard 2500 diaphragm and an electrolyte of 1 mol / L LiTFSI and 2% LiNO3 in DOL+DME (1:1) to assemble a 2032 coin cell in a glove box. First, in the voltage range of 0-1V, use a constant current of 0.5 mA·cm -2 to activate for 5 cycles. After stabilizing the SEI film, perform charge and discharge at a constant current density of 1.0 mA·cm -2 The charging cut-off voltage is 1V. Under repeated charge and discharge conditions, the Coulomb efficiency and the number of cycles are tested. The detection results of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 1 below, and the Coulomb efficiency is as Figure 6 shown.

[0112] According to Figure 6 the Coulomb efficiency diagram shown and the half-cell test results shown in Table 1, it can be seen that by generating two-dimensional nanosheets on the surface of the lithium metal negative electrode current collector to effectively disperse the current density, and using carbon deposition to improve the stability and lithiophilicity of the two-dimensional nanosheets, a good SEI film is formed by the reaction of lithium metal with the nanosheets on the current collector, and the main components are LiF, LiOH and LiC6, which inhibits the growth of lithium dendrites on the surface of the current collector and makes the cycle performance of the battery stable and improved. The lithium metal negative electrode current collector of Example 1 has 900 cycles at a current density of 1 mA·cm -2 and the Coulomb efficiency is maintained above 97%; while Comparative Example 1 fails after 100 cycles; the lithium metal negative electrode current collector of Comparative Example 2 fails after 160 cycles at a current density of 1 mA·cm -2 The cycle performance of the battery in Example 1 is greatly improved compared with Comparative Example 1 and Comparative Example 2.

[0113] Example 7: Symmetric Battery Test

[0114] Prepare 2032 button cells using the same steps as in the half-cell test. First, in the voltage range of 0 - 1V, first use a constant current density of 0.5 mA·cm -2 to activate for 5 cycles at a constant current density, and after stabilizing the SEI film, discharge at a constant current density of 0.5 mA·cm -2 for 20 h at a constant current density, and then charge and discharge at a constant current density of 1.0 mA·cm-2, with the charge and discharge times each being 1 h. Test under repeated charge and discharge conditions to obtain the nucleation overpotential diagram as shown in Figure 5 and the time-voltage curve as shown in Figure 7 .

[0115] According to Figure 5 the nucleation overpotential diagram shown and the half-cell test results shown in Table 1, the nucleation overpotential of Example 1 is about 17.7 eV, while the nucleation overpotential of Comparative Example 1 is about 78.9 eV, and the nucleation overpotential of Comparative Example 2 is about 21.5. Example 1 can effectively reduce the nucleation overpotential of the current collector, and the reduction effect of Example 1 is significantly better than that of Comparative Example 2, indicating that the carbon coating method improves the lithiophilicity of the nanosheets, which is beneficial to the combination of the nanosheets and Li, thus beneficial to the uniform deposition of Li and inhibiting dendrite growth.

[0116] According to Figure 7 the voltage-time curve shown and the half-cell test results shown in Table 1, for the lithium metal negative electrode current collector of Example 1, under the conditions of a current density of 1 mA·cm -2 and a deposition amount of 1 mAh·cm -2 , the overpotential is 14 mV, and the cycle exceeds 2300 h without short circuit. The overpotential of Comparative Example 1 increases significantly with the cycle time and cannot stably cycle within 600 h of the cycle time. For the lithium metal negative electrode current collector of Comparative Example 2, under the conditions of a current density of 1 mA·cm -2 and a deposition amount of 1 mAh·cm -2 , the overpotential is 16 mV, and the cycle exceeds 1600 h without short circuit. The battery cycle performance of Example 1 is greatly improved compared with Comparative Example 1 and Comparative Example 2.

[0117] Table 1. Performance Test Data Sheet of Different Current Collectors

[0118]

[0119]

[0120] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included within the protection scope of the present application.

Claims

1. A three-dimensional composite current collector for a lithium metal anode, characterized in that, It includes a porous metal foam and at least a layer of nano metal hydroxide bonded to the porous surface of the metal foam. On the surface of the nano metal hydroxide layer facing away from the metal foam, there is also a carbon layer bonded, and the carbon layer coats the nano metal hydroxide layer. The nano metal hydroxide particles in the nano metal hydroxide layer are nano-sheets, the carbon layer is two-dimensional nano-carbon, the two-dimensional nano-carbon includes vertically standing graphene, and the vertically standing graphene is composed of self-assembled and vertically oriented multi-layer graphene sheets. The nano metal hydroxide layer includes at least one of a nano nickel hydroxide layer, a nano aluminum hydroxide layer, a nano magnesium hydroxide layer, a nano vanadium hydroxide layer, a nano cobalt hydroxide layer, a nano molybdenum hydroxide layer, a nano iron hydroxide layer, and a nano zinc hydroxide layer.

2. The three-dimensional composite current collector according to claim 1, wherein The metal foam includes at least one of nickel foam, aluminum foam, and copper foam.

3. A method for preparing a three-dimensional composite current collector for a lithium metal negative electrode as described in claim 1 or 2, characterized in that, It includes the following steps: Perform a precipitation reaction on the metal foam, soluble metal salt, and pH regulator in a solvent to obtain a nano metal hydroxide / metal foam composite current collector; perform carbon layer deposition treatment on the nano metal hydroxide / metal foam composite current collector to obtain a carbon-coated nano metal hydroxide / metal foam composite current collector.

4. The preparation method according to claim 3, characterized in that, The precipitation reaction is a hydrothermal reaction; and / or When performing the precipitation reaction, a morphology regulator is also added to the solvent; and / or The pH of the precipitation reaction is 10 to 11, and the reaction temperature is 50°C to 120°C; and / or The carbon layer deposition treatment is carried out in carbon hydrogen gas; and / or The treatment temperature of the carbon layer deposition treatment is 300°C to 900°C.

5. The preparation method according to claim 3 or 4, characterized in that, The soluble metal salt includes at least one of a soluble nickel salt, a soluble aluminum salt, a soluble magnesium salt, a soluble vanadium salt, a soluble cobalt salt, a soluble molybdenum salt, a soluble iron salt, and a soluble zinc salt; and / or The pH regulator includes at least one of hexamethylenetetramine, urea, thiourea, ammonia water, and nickel hydroxide solution; and / or The solvent includes at least one of deionized water, ethylene glycol, and N,N-dimethylformamide.

6. The preparation method according to claim 4, characterized in that, The morphology regulator includes at least one of ammonium fluoride and polyvinylpyrrolidone.

7. The preparation method according to claim 4, characterized in that, The carbon hydrogen gas includes at least one of methane and acetylene gas.

8. A negative electrode of a lithium battery, characterized in that, It includes the three-dimensional composite current collector of the lithium metal negative electrode described in claim 1 or 2 and / or the three-dimensional composite current collector prepared by the preparation method of the three-dimensional composite current collector of the lithium metal negative electrode described in any one of claims 3 to 7, the SEI film formed on the surface of the three-dimensional composite current collector, and the lithium metal attached to the side of the SEI film facing away from the three-dimensional composite current collector.

9. A secondary battery, characterized in that, It includes the lithium battery negative electrode described in claim 8.

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